Safety switch



, July 1944- T. STEVENSON ET AL SAFETY SWITCH Filed April 8, 1942 gvwvwbow Thumua fitayanann EJE rrLurd Vulin Patented July 4, 1944 .2,s52,s64 v sArnrY SWITCH OFFICE.

Thomas Stevenson and Bernard volin,

Philadelphia, Pa.

Application April 8, 19 12; Serial No. 438,062

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to safety switches and more particularly to switches which interrupt current in the vicinity of explosive atmospheres.

An object of this invention is to provide a switch which automatically shuts off a heater when the temperature in the area being heated becomes too high.

Further, it is an object to provide a thermostatically controlled switch without the use of bimetallic strips which might conceivably stick and fail.

Another object of this invention is to provide a safe thermostatically controlled switch in which there is no possibility of arcing and in which heating currents do not flow through temperature responsive elements thus avoiding the possibility of premature interruption of the switch.

Another object of this invention is to provide a temperature responsive switch in which the contacts thereof are enclosed in a chamber and joined by a fusible element which is responsive to ambient temperatures foi its fusibility.

The specificnature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Figure 1 discloses a preferred form of my invention and also discloses a mercury switch pivotally mounted on an arm with the free end of the arm supported by a fusible element I2.

Figure 2 discloses an arrangement similar to that shown in Fig. 1 but in this instance the mercury switch is pivoted nearer its center.

Figure 3 discloses a pair of spaced and enclosed switch contacts 10, II joined by temperature responsive material 12.

Figure 4 discloses an arrangement similar to those shown in Figs. 1 and 2 but in this instance the mercury container 45 is open and surrounded by the closed chamber 4 I.

Figure 5 discloses an arrangement similar to the one shown in Fig. 3 but in this instance the switch contacts 60, 6| are spring biased away from one another when the element 64 melts due to high ambient temperature.

In Fig. l mercury switch 4 having all of its essential elements contained in a glass envelope 5 is mounted on arm 3 which is pivoted about shaft 2 on support I and supported by temperature responsive fusible element I2. The mercury switch 4 includes the spaced contacts 6, I which are connected to binding posts I0, II by means of conductors 8, 9. A weight I4 assures positive interruption of the fusible element I 2 when the ambient temperature rises to a predetermined value, thus causing a tilting of the switch 4 and a consequent opening of the switch contacts 6, 1. The contacts 6, I are connected in series with an electrical heating element (not shown) which heats the air surrounding element I2. It is thus seen that if the ambient temperature rises the current to the heating element will be interrupted without extraneous arcing.

In the modification shown in Fig. 2 an enclosed mercury switch 24 similar to the one shown in Fig. 1 is pivotally mounted about shaft 22 on support 2| with the weight 34 and temperature responsive fusible element 32 on opposite sides of the switch envelope 25. Envelope 25 is mounted on arm 23 and moves therewith. Leads 28, 29 extend to a heating element (not shown), which heats the air surrounding fusible element 32.

In Fig. 3 the glass envelope l3 encloses the fixedly mounted and spaced contacts I0, 1| which are joined by temperature responsive fusible material I2. The envelope 13 might be partially evacuated or have a high pressure filling of air or gas therein. Contacts III, II extend to an electrical heating element (not shown) and when that electrical heating element causes the ambient temperature surrounding envelope 13 to rise above a predetermined value, fusible element I2 will melt and the current to the electrical heating element will be interrupted without the presence of arcing in the vicinity of the atmosphere surrounding envelope I3.

In Fig. 4 the mercury container 45 is open but the entire switch assembly is enclosed by container 4|. Leads 48, 49 are in series with an electrical heating element (not shown). When the temperature within chamber 4I reaches a predetermined value fusible element 52 will melt and lead 48 will be pulled out of the mercury 153201 by the action of prestressed tension spring In the arrangement shown in Fig. 5 leads 80, SI are in series with an electrical heating element (not shown) and are held in spaced relationship by means of ambient temperature responsive fusible element 64. When the ambient temperature within enclosing container reaches a predetermined value, switch contacts 60, 6| are positively separated one from the other by the action of prestressed tension springs 62, 63.

The ambient temperature responsive elements able due to the possibility of failure. It should,

be understood that switches as disclosed in Figs. 1-5 are not intended to supplant conventional thermostatic control but are designed to supplement such equipment and provide an extra 15 safety factor.

We claim:

In a device of the character described, a sup port, a body of ambient temperature responsive fusible conducting material, a pair of contact wires embedded in said body, a stressed coil spring secured to said support adjacent to and on each side of said body and having connection with said wires, one spring being connected to one side of the support and the other to the 0pm posite side thereof and exerting their force in opposite directions to accelerate the separation of the contacts during and after the fusing of the fusible body.

' THOMAS STEVENSON.

BERNARD VOLIN. 

